1. Field of the Invention
The present invention is directed to devices and methods for interrupting capillary flow of liquid between two pieces of bibulous material which, prior to actuation, are in a capillary flow relationship to each other. In particular, the device is actuated and the capillary flow relationship between two pieces of bibulous material is interrupted by utilizing a liquid expandable piece of bibulous material. When actuated by wetting, the liquid expandable piece of bibulous material interrupts capillary flow between two pieces of bibulous material by separating these two pieces which interrupts their capillary flow relationship. The methods and devices of the present invention have particular utility in assays which require transport over set times or of set volumes of solutions and/or samples by capillarity. Such assays include, for example, enzyme immunoassays, fluorescent immunoassays, radioimmunoassays, etc.
2. Related Art
Assay devices have been described in which liquid is transported by capillarity through or transversely along a bibulous support thereby transporting reagents and samples to sites on the support and/or washing the support. Such devices have been described by Deutsch, U.S. Pat. No. 4,094,647; Zuk et al, U.S. Pat. No. 4,435,504; Weng et al, U.S. Pat. No. 4,740,468; Friesen et al, German Offenlengungschrift 3,445,816, etc.
In many of these methods, a specified amount of a liquid reagent is added to the bibulous support. In such situations, it is desirable for a liquid reagent moving along a bibulous support to automatically stop moving after the specified volume of this reagent has been taken up so as to avoid the necessity of monitoring the flow of this reagent.
In the past, the flow can be stopped by limiting the length of the bibulous material. However, this approach requires that assays utilizing different amounts of liquid reagent utilize different lengths of bibulous material (assuming of course that all the other variables, such as the thickness of the bibulous material, etc. are the same). However, use of different lengths of bibulous material is substantially less efficient than a system which controls the amount of liquid reagent added to the bibulous support regardless of its length because the latter would permit the use of standardized lengths of bibulous material in assays requiring uptake of different amounts of liquid reagents. Moreover, the use of standardize lengths of bibulous materials would permit the use of standardize devices such as that depicted in U.S. Ser. No. 35,562 now U.S. Pat. No. 4,857,453 filed on Apr. 7, 1987 entitled "Immunoassay Devices" which is incorporated herein in its entirety.
Accordingly, it is desirable to interrupt the capillary flow of liquid between two pieces of bibulous material which theretofore were in a capillary flow relationship to each other after a specified amount of reagent has been taken up by the pieces of bibulous material. Moreover, it would be particularly desirable to interrupt such a capillary flow relationship automatically without mechanical means external to the device while requiring little or no operator involvement.
U.S. Pat. No. 3,482,943 discloses expandable sponges useful in transporting solution to a set position on a gel suitable for conducting immunodiffusion tests. In this reference, the solution transported by the sponge is allowed to diffuse into the gel which, in order to conduct the immunodiffusion, is by necessity a wet gel. Accordingly, no capillary flow relationship between the expandable sponge and the gel is established by this device.
U.S. Pat. No. 4,246,339 discloses a device having an upper portion and a lower portion. The upper portion has a plurality of wells wherein the bottom of each well is fitted with a membrane layer capable of transporting liquid. The bottom portion of the device contains absorbent material. Between the top and bottom portions is a compressible spacer. This device allows a liquid sample to be added to the wells which may optionally be impregnated with an antibody. After a set incubation period, pressure is placed on the top portion which because of the compressible spacer, allows the bottom of each of the wells to contact the absorbent material whereupon the liquid in the wells is transferred to the absorbent material. After liquid transfer, the pressure is removed and contact between the bottom of the wells and the absorbent material is broken. Thereupon, additional liquid may be added to the wells. In this device, care must be taken to insure that the bottom of all of the wells come into contact with the absorbent material for a sufficient period of time to remove the liquid. In particular, if one or more of the wells does not contact the absorbent material, then the liquid in that well will not be removed. Moreover, if one or more of the wells does not contact the absorbent material for a sufficient period of time, then not all of the liquid in that well will be removed. In any case, a high level of operator care is required to ensure the proper operation of this device.
U.S. Ser. No. 35,562 filed Apr. 7, 1987 entitled "Immunoassay Devices" discloses a device for conducting an assay method. The device comprises a housing having in one portion thereof a breakable capsule and in another portion a piece of bibulous material attached to an absorbent pad. However, this reference neither teaches or suggests the use of a liquid expandable piece of bibulous material which, when desired, can interrupt capillary flow relationship between two pieces of bibulous material.
European Patent Application Publication No. 0 146 691 discloses an air bleed passage in a liquid sampling needle which is formed between a housing and a sleeve and into which is added a solid compacted material which swells on contact with liquid. As the liquid sample is drawn into the needle, air can escape via the air bleed until the air bleed is contacted with liquid whereupon it expands and forms a liquid impermeable membrane.
U.S. Pat. No. 4,700,741 discloses a urine collecting device which contains an expandable sponge in a compartment which permits the collection of a predetermined quantity of urine by limiting expansion of the sponge within the compartment.
Canadian Patent No. 1,185,882 discloses porous hydrophilic, non-gel-forming swellable polymers as self-drawing fluid reservoirs with a very high and uniform absorption and release of fluid in a chromatographic quick-test device.
U.S. Pat. No. 4,826,759 describes apparatuses and methods, which can be used in the field (i.e., outside the laboratory environment) to determine qualitatively and at least semiquantitatively the presence or absence of minute quantities of ligand. The apparatus can be in the form of a strip comprising a support means provided with a groove intermediate its ends forming a crease line upon which the strip can be folded upon itself with bibulous elements and spaced from the crease line and arranged so that when the strip is folded upon itself the bibulous elements become aligned with each other and come into liquid contact.
U.S. Pat. No. 4,803,170 discusses an immunoassay device including one or more reaction chambers, each adapted to receive and retain a volume of test fluid in fluid communication with nonoverlapping first, second, and third reagent-bearing surfaces. To the first surface is reversibly bound an analyte conjugate: analyte component conjugated to one or more components, termed ligand/marker, that serve ligand and marker functions as described herein. Analyte binding partner is immobilized on the second surface, and ligand/marker binding partner is immobilized on the third surface. The reaction chamber is preferably configured to receive and direct the test fluid sequentially past the first, second, and third reagent surfaces. In use, analyte conjugate solubilized from the first surface completes with any analyte in the test fluid for analyte binding partner sites on the second surface. Excess analyte conjugate becomes sequestered on the third surface, where the marker activity is read to indicate analyte presence and concentration in the test fluid. A test kit includes the immunoassay device in combination with comparative test results.
Accordingly, there is a need for a device for interrupting a capillary flow relationship between two pieces of bibulous material which prior to actuation are in a capillary flow relationship to each other. Preferably, such a device would automatically interrupt this capillary flow relationship after a specified amount of liquid has been taken up and would require little or no operator involvement to actuate.